Provisional Games

Could someone explain further how the ranking system works at the beginning at the season. I have been doing ranked since s4 and i was placed in bronze 4. I understand that I wasn't as good of a player, season 5 I got placed in bronze 4-3 I can't remember. After winning 3 out of 10. I understand that and in the games that I won i was carried. This season I won 5 out of my ten going 21-11 in one game and 16-11 in another. I also varied roles and helped carry my team. I was put into bronze 5. So could someone please help me to understand how that may have happened? I just want to clarify i am not mad or raging I would just like some further information. Thank you very much, your fellow summoner Ajmonster101